1. Field of the Invention
The present invention relates to a data recording/reproduction method and a data recording/reproduction method for performing at least one of a recording process and a reproducing process on an optical disk, and more particularly to a data recording/reproduction method and a data recording/reproduction method conducting focus control during a data recording/reproduction operation.
2. Description of the Related Art
Common optical disks (e.g., CD, DVD, Blu-ray disc, HD-DVD) that are widely used for reproducing data and/or writing data are configured with a polycarbonate resin substrate having a diameter of 120 mm and a thickness of 1.2 mm. In a case where a common optical disk is rotated by a common disk drive apparatus, the optical disk exhibits an axial runout (surface vibration) reaching an amount ranging from 50 μmP-P to 300 μmP-P in the vicinity of its outermost periphery.
Along with the disk drive apparatus, an optical disk recording/reproducing apparatus is also provided with an optical pickup for recording data into an optical disk and/or reproducing data recorded in the optical disk. The optical pickup is configured to detect reproduction signals and control signals by irradiating and condensing an optical beam to a beam spot on the optical disk while conducting focus control and receiving an optical beam reflected to its optical element from the optical disk.
At the beginning of the focus control, a pull-in process of the focus servo is performed. The pull-in process is performed by determining the S-curve formed by a focus error signal. For example, the flowchart of FIG. 7 shows operations performed with the pull-in process.
As shown in FIG. 7, an optical disk is loaded into a disk drive apparatus (Step S1). Then, the loaded optical disk is rotated (Step S2). Then, an optical pickup irradiates an optical beam onto the optical disk and moves an objective lens toward the optical disk for focusing the irradiated beam on a recording surface of the optical disk. At this stage, since axial runout in the above-described amount occurs in the optical disk, the detected focus error signal generates a waveform shaped as an S-letter curve (see (a) of FIG. 8) having the focal point as its center (Step S3). Then, the S-letter curve is monitored for detecting a zero-crossing point. Upon detecting the zero-crossing point, the position of the optical beam is determined, that is, pull-in for a subsequent focus control operation is conducted (Step S4).
Then, a focus control operation is conducted (Step S5). Then, a tracking control operation is conducted (Step S6). After a stable position is maintained for the optical beam by the tracking control operation, a process of recording/reproducing data is conducted (Step S7).
As an example of the optical disk recording/reproducing apparatus, an optical disk recording/reproducing apparatus using a flexible optical disk is disclosed in Japanese Laid-Open Patent Application No. 2006-107698. This optical disk recording/reproducing apparatus is configured to reduce axial runout by using a stabilizing member for applying aerodynamic force to the flexible optical disk. In a case where a thin optical disk having a thickness ranging from 0.08 mm to 0.2 mm is used in this optical disk recording/reproducing apparatus, although the amount of axial runout increases from the innermost periphery to the outermost periphery of the optical disk, the maximum amount of axial runout exhibited by the optical disk ranges from 1 μmP-P to 10 μmP-P. The amount of axial runout exhibited by the optical disk is approximately 1/10  to 1/300 compared to that of the common existing optical disk. Thus, axial runout is significantly reduced with the optical disk recording/reproducing apparatus.
As one example of a focus control method performed on the flexible optical disk, Japanese Laid-Open Patent Application No. 2002-358759 discloses a method in which focus control is performed after obtaining a predetermined height by adjusting the amount of a stabilizing member projecting with respect to an optical disk and detecting an S-curve of a focus error signal.
With the configuration disclosed in Japanese Laid-Open Patent Application No. 2006-107698, a constantly occurring disturbance can be reduced during a focus control operation after a pull-in process. Particularly, the focus error amount during high speed rotation of an optical disk can be reduced, to thereby enable a suitable focus control operation during the high speed rotation.
However, in the focus control operation, the small axial runout having a maximum amount ranging from 1 μmP-P to 10 μmP-P makes it difficult for the focus error signal to form a clear distinctive S-curve. As shown in (b) of FIG. 8, this configuration forms an inconsistent extremely low level S-curve. This causes difficulty in performing the pull-in process.
With the method disclosed in Japanese Laid-Open Patent Application No. 2002-358759, since the amount of projection of the stabilizing member with respect to the optical disk is adjusted prior to the focus control operation, the stabilizing member may contact the optical disk depending on the amount of the projection. Furthermore, an S-curve may not be consistently formed by using this method.